The present invention relates to a device for manufacturing a groove bearing having a bearing shaft and a bearing bush with cooperating bearing surfaces, of which at least one bearing surface is formed with a pattern of pumping grooves.
A device for forming such grooves has been taught in EPA2292. This device, shown in FIG. 1 hereof, comprises a hard pin 1 around which a cylindrical cage 2 is arranged which has one or more annular patterns of holes arranged symmetrically about the central axis of the cage. These holes are engaged by hard balls 4 having a diameter larger than the wall thickness of the cage. The cage and the pin or sleeve are each coupled to a drive arrangement capable of impressing a translation and a rotation upon the cage and the pin or sleeve. Thus, the cage 2 and pin 1 are separately translated and/or rotated in order to form the grooves 6 in the surface of the bearing wall 5.
According to the patent owner's own later filed U.S. Pat. No. 5,265,334, it has been found that in carrying out the prior art method that the pin or sleeve of the prior art device is subjected to substantial wear as a result of large Hertzian stresses produced at the contact surfaces between the pin or sleeve and the balls. The wear particularly causes deformations of the pin surfaces surrounding and facing the cage, so that the contact surface of the pin or sleeve becomes irregular resulting in inaccurate groove depth. Therefore, this same U.S. Patent '334 discloses a improvement shown in FIG. 2 of the present application in which the bearing surface of the bearing part (which may be a pin or sleeve) includes a continuous groove 7 which is concentric with the central axis of the pin or sleeve, the groove extending in a longitudinal sectional plane of the pin 1 which contains the central axis. Either the pin 1 or cage 2 is then exclusively both rotated and translated to form the grooves 6.
It has further been found that it is difficult to form the grooves by driving either the pin or the cage in both rotation and translation without the development of application specific, expensive machinery.
Also, the equipment and device as described above, and other known devices in the field, have been unable to successfully groove steel on a reliable basis. As a result, hydrodynamic bearings in motors developed to date have been typically formed of softer materials such as brass, limiting their lifetime. The development of a device and method for successfully grooving steel would lead to less expensive hydrodynamic bearing and hydrodynamic bearing equipped motors, and bearings having a longer lifetime.